Scientists putting NASA's latest space telescope through its paces have found something odd - a pulsar emitting in gamma rays.

The discovery, published in this week's issue of Science, is the first finding from NASA's Fermi Gamma Ray Space Telescope, which was launched in June.

It solves a mystery uncovered by a predecessor telescope and offers an explanation to a host of similar unexplained phenomena.

The pulsar detected by Fermi is associated with a supernova remnant known as CTA 1, the remains of a massive star in the Milky Way galaxy that exploded about 10,000 years ago. It is located about 4600 light-years away in the constellation Cepheus.

Typically, supernova remains include the dead star's collapsed core - known as a neutron star, because its protons and electrons have combined to form neutrons.

Sometimes the neutron star is spinning, which causes jets of particles to stream out above their magnetic poles, producing powerful beams of light that appear as flashes as the star rotates.

These are known as pulsars, and their beams have been found in radio wavelengths, x-ray and, now for the first time, in gamma rays as well.

"Our idea is that the gamma ray beam is much wider (than other forms of electromagnetic radiation) so we're able to see it," says Alice Harding of NASA's Goddard Space Flight Center. "If that's true it means we should be finding lots more of these."

Searching for more

The first gamma ray pulses from the vicinity of CTA 1 were detected on 11 July, a week after astronomers began viewing the sky with Fermi.

The discovery was later confirmed during follow-up observations. The pulses sweep toward Earth about three times per second.

Scientists knew from a previous gamma ray telescope that the remnant held something unusual.

"Nobody knew where it was coming from," says Harding. "We decided to look for pulsations, and we saw a particular time pattern in the arrival of the gamma rays. They were arriving in pulses."

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